Gene therapy approaches involving constitutive overexpression of cDNAs encoding individual BMPs can induce bone formation and partially repair cranial and long bone defects as shown by this laboratory. However, this strategy is limited by the availability of BMP-responsive osteoprogenitor/stem cells at the regeneration site and lack of control over the timing and duration of regenerative factor expression. The underlying hypothesis of this competitive renewal is that bone regeneration can be greatly improved if gene therapy is used to mimic the natural processes of bone development and fracture repair characterized by the participation of multiple growth/differentiation factors whose expression is under tight temporal control. Of particular importance are factors such as BMPs that may function as heterodimers to stimulate progenitor differentiation and FGF2 that controls progenitor proliferation. This project, which contains both translational and basic science components, will compare the efficacy of regenerative approaches in well-defined preclinical models as well as explore underlying mechanisms by achieving the following specific aims: Aim 1. Evaluate actions of an adenovirus expressing FGF2 (AdFGF2) on osteoprogenitor cell proliferation and differentiation in vitro and in vivo with or without Ad BMPs. Hypothesis: AdFGF2 can expand the population of osteogenic precursors at regeneration sites to enhance bone formation. Aim 2. Use inducible gene expression systems to control the timing, duration and sequence of osteogenic factor synthesis. Hypothesis: Enhanced control of osteogenesis can be achieved using regulated gene expression to control the timing, duration and sequence of proliferative versus osteoqenic signals. This project will test novel regenerative concepts involving cooperative interactions between proliferative and osteogenic factors and temporal regulation of factor synthesis using simple rodent models. Approaches developed will provide proof of principle of the eventual development of new therapies for bone regeneration that mimic natural biological processes by providing temporal control over regenerative events.